Apparatus for determining the dew point of a vapor product



1938- R. F. DENISTON ET AL 2,106,593

APPARATUS FOR DETERMINING THE DEW POINT OF A VAPOR PRODUCT Filed May 5,1936 2 Sheets-Sheet 1 0/5771 1 A TE INVENTORJ W @mlmawg ORNEY Jan. 25,1938. R. F. DENISTON ET AL 2,106,593

APPARATUS FOR DETERMINING THE DEW POINT OF A VAPOR PRODUCT Filed May 5,1956 2 Sheets-Sheet 2 CONTROLLER 1 /0 Eff/DUE L M MQ INVENTORJ BY Z 2IZATTORNEY Patented Jan. 25, 1938 UNITED STATES PATENT OFFICE APPARATUSFOR DETERMINING THE DEW POINT OF A VAPOR PRODUCT Application May 5,1936, Serial No. 77,942

2 Claims.

This invention relates to a device for continuously testing theproductoi' a continuously operating distilling, stabilizing, orfractionatin device.

An object of this invention is to provide a device capable ofassociation with a iractionating device to continuously observe the dewpoint,.or temperature of total equilibrium vaporization of the productof such apparatus.

Another object is to permit the observation of such quality in such amanner as to permit it to be used for control oi the operation producingthe product. Other objects and advantages are possessed by thisinvention, some of which will be referred to hereinafter and some ofwhich will be obvious to those skilled in the art.

While pertinent to all distillation operations in which the end boilingpoint of the product must be controlled to avoid the inclusion ofmaterials 50 heavier than desired, the discussion will be herein limitedto motor gasoline for simplicity. Most of the desirable properties ofgasoline are tied up with its end distillation point and its volatility.So great is the truth of this statement that freetionating equipment forthe production of gasoline is practically always operated by the controlof end boiling point on the one hand and total vapor pressure on theother. Methods for automatically observing, and recording total vaporpressure and basing the control onthat have been worked out forapplication to stabilizers and similar apparatus for the reduction ofvolatility or vapor pressure in excess of that desired. No

simple method has as yet been presented for the automatic control-oi endboiling point.

Methods at present used for the control of end boiling point involveperiodic removal of a sample, manual distillation in a batch process-theA. S. T. M. distillation, interpretation of results,

and subsequent change of distillation conditions if the control test hasshown this to be necessary. This method presents several difllculties.Considerable time elapses between tests, manual control is involved, anda chemists time is required for the distillation. The results 01' thetest are not, in themselves, a direct measure of the characteristicsdesirable in the product. The nearest approach to automatic operation ofwhich we are aware accomplishes automatic withdrawal and analysis ofsample, but leaves the entire interpretation of results and adjustmentfor correction just where it was before.

This invention is based upon the discovery that 55 the dew point of aproduct may be continuously observed in a convenient manner, and thecontrol of equipment automatically accomplished thereby.

The dew point oi. a vapor is the temperature at which initialcondensation occurs when a whole,

completely vaporized sample is'cooled. Converse- 1y, when considering amaterial such as gasoline, which has a boiling range rather than aboiling point, it is the temperature at which a sample heated undernon-vaporizing conditions, will just be 100% vaporized on releasing or"flashing." The dew point is thus a comparatively sensitive measure ofheavy material in the product. It has the advantage of having a directphysical significance. Carburetion in an internal combustion engine, oranalogous operations, are in reality flash vaporizations. equilibriumflash vaporization point, is directly responsible for completeness ofvaporization under any given conditions and easily correlated therewith.No other commonly observed property is so directly a measure of thisvaluable characteristic of gasoline. Vapor pressure alone is only partof the story, because vapor pressure is highly sensitive to percentageof highly volatile components, and relatively insensible to high boilingcomponents. A. S. T. M. distillation end point is not completelysignificant, because two gasolines of the same end point will varygreatly in ability to be volatilized under given conditions because ofvariation in relative amount oi! lighter components present. These twoproperties bear upon each other and thus compel interpretation oi.results and prevent simple automatic control from observation of suchproperties. Dew point is the one determinable property which ties thesethings together, and when it becomes possible to continuously observeand record the dew point, it is possible to continuously control stillconditions in a simple and convenient manner without the necessity of anoperator's interpretation of results.

We have devised an apparatus for continuously observing and recordingthe dew point and which lends itseli to such control. In order that thisdevice may be more readily understood, reference is now made to thedrawings attached to and made a part 0! this specification, in whichFigure 1 shows the dew point apparatus and Figure 2 shows the manner inwhich it may be applied to still control.

In Figure 1, which is diagrammatic, 3 is a pipe through which thedistillate product to be tested is introduced in condensed or partiallycondensed form to coil 4, placed in heating bath 6, which is filled witha suitable liquid and heated by The dew point, or 100% iectrlcal heater:lne heated to ell. b a

which is is likewise r vaporate from the pan 3 to the gas stream. bel wthe dew pol the pan regularly be comes hes. --until it filled. Above thedew a 3 becomes lighten-until empty.

in weight pan i3 is employed to cm. temperature of the bath and indiweand record point. Any

nose. 2 e orefe to employ an inductance ce it enables us to dispense witmov springs, etc, mounted. in the vapor stream 5; exposed to possiblegumming and. corrosion. The inductance bridge consists of solenoid coilsl8 surrounding solenoid core M, which supports the pan, and solenoidcoils ll surrounding core i8. The inductance bridge is actuated by asource of alternating current 20, which also supplies the variousheating services. Without considering in detail the makeup of theinductance bridge, which is well known, its properties are such thatwhen actuated by alternating current as shown, the two cores aresuspended at certain points as determined by their weights, theproperties of the coils, etc., and any change in the position of one isfollowed by a corresponding proportional change in the position of theother. Thus, when coil 1 is below the dew point and pan l3 becomesheavy, core l4 moves down, and a corresponding movement of core i8relayed by contacts l9 admits current to auxiliary heater 2!. When coil1 is above the dew point, pan 13 becomes lighter, and core I8 iscorrespondingly moved to cut out heater II. The bath in heating vessel 8and coil 1 immersed therein are thus kept at the dew point of the vaporanalyzed, proportions of bath and coil being so selected that hunting isminimized. It is of course understood that while direct contacts areshown at I9, it will probably be preferable to employ some convenientform of relay system, the direct contacts being shown for simplicity.Since the bath in vessel 8 is maintained at the dew point of thesubstance analyzed, it is simple to observe the temperature of the bathor in the trap ID by any convenient form oi thermocouple as 22, hereshown in the bath near trap ID, to which is attached the indicating andrecording pyrometer designated by 23.

in diagrammatic form how this dew point, in this apparatus r the controlof a distillation gure 24 is a. columnar still, to which feed reduced bypipe 26, and heated by coal Residue is withdrawn through pipe ET, v "orspass overhead through pipe 29 to receiver 30. Distillate awn throughpipe 3!, and pipe end a continuous sample of dis point analyzercomprising vessels rap Hi, as previously described. rmocouple 22observes the dew pols; and instrument 23 indicates and records it. Inthis set-up however, instrument 2! has an additional function.Condensate from drum 3!) is returned by pump 33 through pipe 34 as wetre for on rol of top temperature of tower eturned being controlled byvalve 23 in this case is also a control instrument, so designed thatwhen the dew point exceeds a predetermined maximum, admitted to tower24, and when too low, less is admitted. capable of so acting are own,and of many forms, and 1' part of this invention, and motion isconsequently indicated onnection between instrument 23 r vur l productis 32 is provide.' tillate to a use i that equivalents of the devicedisclosed will occur to those skilled in the art, and it our intentionto claim all that is move} 5. ermn, except as limited by the followingclaims.

We claim:

Means for continuously observing the dew point of a continuously flowingstream of vaporizable substance comprising means Ior continuouslysampling said stream, means for converting said sample to a slightlysuperheated vapor, a tube through which said vapor flows, a heater tomaintain said tube at a temperature below the dew point of said vapor,said tube including a trap, pan in said trap, means to direct condensateformed in said tube on said pan, an auxiliary heater for said tube,means responsive to the weight of the condensate in said pan to controlsaid auxiliary heater to add more heat in response to an increase andless heat in response to a decrease in condensate, whereby said tube ismaintained at the dew point temperature of said vapor, and means toobserve the temperature of the tube.

2. Means for continuously observing the dew point of a flowing stream ofvaporizable substance, comprlsing means to extract a sample therefrom,means to convert such sample to a slightly superheated vapor, means tocool such vapor to a controlled temperature, means to collect anycondensate so formed in a position exposed to uncondensed vapors, meansactuated by the amount of condensate collected to so control the coolingtemperature that the condensate amount tends neither to decrease norincrease, and means to observe the controlled temperature.

ROBERT F. DENISTON. WENDELL P. HAWTHORNE.

